Vacuum gap devices with helicoidal electrode structure



Uct. 7, 1969 J. A. RICH 3,471,736

VACUUM GAP DEVICES WITH HELICOIDAL ELECTRODE STRUCTURE Filed May 19, 1967 3 Sheets-Sheet 1 /n vemor Joseph A. Rich His Attorney- Oct. 7, 1969 J. A. RICH 3,471,736

VACUUM GAP DEVICES WITH HELICOIDAL ELECTRODBSTRUCTURE Filed May 19, 1967 3 Sheets-Sheet .2

Pulse Source //7 vemar Joseph A. Rich His Arforne y.

0d. 7, 1969 J. A. RICH 3,471,736

VACUUM GAP DEVICES WITH HBLICOIDAL ELECTRODE .STRUCTURE Filed May 19, 1967 3 Sheets-Shea F [2? ve ntor':

do eph A Rich v/s Attcrney.

hired States Patent 0 US. Cl. 313231 8 Claims ABSTRACT OF THE DISCLOSURE Vacuum gap devices, including triggerable gaps and switches, capable of handling extremely high currents without the formation of anode spots are made utilizing electrodes in the configurations of a pair of helicoids occupying the same space and parallel with one another. This electrode structure provides a very large surface area for the interelectrode gaps. All portions of the gaps are equidistant due to the parallel helicoidal structure. Bunching of current paths and the consequent formation of anode spots is avoided by the interleaved parallel helicoidal electrodes since substantially no magnetic field exists in the interelectrode spacing and that field which does exist is in parallel with current conduction paths.

Related applications This application is related to the concurrently filed copending applications, Ser. No. 639,844 of James M. Lafferty, and my concurrently filed co-pending applications, Ser. Nos. 639,843 and 639,693, all of which are assigned to the assignee of the present application.

The present invention relates to vacuum gap devices adapted to operate at high currents without the formation of anode spots therein. More particularly, the present invention relates to triggerable vacuum gap devices and vacuum switches in which the formation of anode spots is avoided by the fabrication of the primary arc-electrodes thereof in the form of a plurality of interleaved helicoids to avoid the formation of anode spots.

In the development of vacuum switches and triggerable vacuum gap devices, a limiting factor to the amount of current which may be drawn by a given structure is the threshold current at which a destructive anode spot is formed. Formation of such anode spots results in erosion of the anode electrode and melting thereof. Such erosion and melting adversely effects they surface of the electrodes, making the breakdown voltage change in the direction of a lower value than its original value, and eventually leading to serious failure. In the development of prior art vacuum gap devices, many attempts have been made to minimize the destructive effect of anode spots. These attempts have, however, generally accepted the proposition that the formation of anode spots is inevitable, and have been directed to the minimizing of the destructive effect of anode spots. Such attempts have been generally in the nature of fabricating the electrodes and applying magnetic fields in such fashion as to cause the anode spot to be continuously moved over various surface portions of the electrode, generally the periphery thereof, to minimize the effect of anode spots upon the breakdown characteristics of the interelectrode gap.

In accord with the discovery set forth in my copending application, Ser. No. 639,693, it is noted that the reason for the formation of anode spots in any given arc-electrode configuration, particularly in configurations in which the area of the arc-electrodes has been made large in order to decrease current density for any given value of current, to minimize the probability of the formation of anode spots, is the fact that most structures of this nature generally result in current conduc- 3,47l,736 Patented Oct. 7, 1969 tion paths between the arc-electrodes that are normal to a component of the magnetic field existing within the device, due to current conduction. Another way of expressing this relationship is that the magnetic fields within the interelectrode gap, due to current conduction path through the device, generally have a component that is orthogonal to the current conduction path across the gap. Because of this relationship a body force acts on a volume of conducting fluid equal to the quantity F XB where I is the current density and B is the fiux density. This force is effective to cause the current conduction paths to move in a direction orthogonal to both the current conduction paths and the normal component of the magnetic field. The result of this force acting upon the current conduction paths is to cause a bunching of current conduction paths at a particular point or region of the electrode, resulting in a very high current density thereat. With the increased current density due to bunching, an anode spot is generally formed and the anode is erosed and/or melted at that particular point or region. Repeated meltings of the anode at the same point or region on repetitive arcing generally results in failure of the device.

Accordingly, it is an object of the present invention to provide vacuum are devices wherein the electrode configuration completely eliminates a force upon current conduction paths between the arc-electrodes resulting in the elimination of bunching thereof.

Yet another object of the presert invention is to provide vacuum are devices having an electrod configuration which completely avoids the formation of anode spots making possible the attainment of high current carrying capacities.

Still another object of the present invention is to provide vacuum are devices having interelectrode structures which substantially eliminates magnetic fields having a component normal to the direction of current conduction between the arc-electrodes.

In accord with the present invention, in one embodiment thereof, 1 provide a vacuum arc device having an evacuable envelope evacuated to a pressure of 10- mm. of Hg or less and having as a portion of the envelope a high voltage dielectric. Within the envelope of this device I provide a pair of primary arc-electrodes in the form of interleaved continuously parallel helicoidal surfaces, one of which is connected to each pole of a source of voltage applied in circuit with the device. Because magnetic fields due ot the current conduction within the arc-electrodes are substantially eliminated from the interelectrode gaps, and because any residual magnetic fields which exists in the gaps are parallel to the current conduction paths therein, no body force acts upon the current conducting plasma, the bnnching of current conduction paths between the arc-electrodes is essentially eliminated and anode spots do not form, thereby greatly increasing the current capacity of the device.

The novel features believed characteristic of the present invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood with reference to the following description, taken in connection with the appended drawings in which:

FIGURE 1 is a vertical cross-sectional view of a triggerable vacuum gap device constructed in accord with the present invention,

FIGURE 2 is a vertical cross-sectional view of a vacuum switch constructed in accord with the present invention, and

FIGURES 3 and 4 are embodiments of a vacuum gap device constructed in accord with the present invention which incorporate both a vacuum switch and a triggerable vacuum gap device.

In vacuum arc devices, the current threshold marking the onset of the formation of anode spots is a function of electrode geometry and electrode material. For a given material, therefore, the formation of anode spots is a function of electrode geometry. In the plane-parallel geometry, frequently utilized in switches and vacuum gap devices, the threshold is relatively low since a spot is formed at any point at which the current density becomes high, either due to surface irregularities or anchoring of the are due to the interaction of electric and magnetic fields. One means for inhibiting the formation of anode spots is to greatly increase the active arc-electrode area so that the current density at any given point is much less than it would be for the same value of current with a lesser area of the electrodes at the interelectrode gap. Another means utilized to minimize the deleterious effect due to anode spots, which means is often utilized in connection with the increase in area of the arc-electrodes, is to cause the magnetic fields existing within the interelectrode gap, either by virtue of the current path traversed by current in the device or by the application of external magnetic fields, to interact with the current conduction path of the arc to cause rotation thereof, thus minimizing the heating and erosion of any given point traversed by the anode spot. While such attempts have greatly improved the current carrying capacities of vacuum switches and triggerable vacuum gap devices constructed in accord with these principles, such attempts always prolong failure of the device, but do not eliminate it, since eventually even moving arcs do cause sufficient erosion as to deleteriously effect breakdown characteristics of the device.

In accord with my co-pending, concurrently filed applications mentioned hereinbefore, I have discovered and have disclosed various arrangements of electrode geometries in which the formation of anode spots is inhibities. The inventions set forth in the aforementioned applications are based upon my discovery that the formation of anode spots is due to the bunching of current conduction paths in broad area interelectrode gaps due to a body force acting upon current conducting plasma due to the vector product of the current and the normal component of the magnetic field existing within the gap. Generally,

' this normal component of magnetic field existing within the interelectrode gap is due to the path of current conduction within the electrodes because of the configuration of the electrodes utilized to form a large area interelectrode gap. In accord with the present invention, I have discovered a unique electrode configuration which serves the purpose of greatly increasing the area of the interelectrode gap, while at the same time arranging the current conduction paths between the primary arc-electrodes so that essentially no magnetic field exists within the interelectrode gap and any magnetic field which does exist Within the gap is essentially parallel to the conduction paths, so that the vector product J B equals or approximates zero.

FIGURE 1 of the drawing illustrates, in vertical crosssection, a triggerable vacuum gap device constructed in accord with the present invention. In FIGURE 1, triggerable vacuum gap device includes a first electrode assembly 11 and a second electrode assembly 12 surrounded by a metallic cylindrical sidewall member 13 which is joined by an insulating, dielectric seal member 14, which both provides electrical isolation between electrode assembly 11 and electrode assembly 12 and completes an hermetic seal to completely enclose the envelope of device 10. First electrode assembly 11 includes a substantially planar base member 15 and a downwardly-depending right helicoid 16 having an upper surface 17 and a lower surface 18. Second electrode assembly 12 includes a lower base member 19 and an upwardly-depending right helcoid 20 having a lower surface 21 and an upper surface 22. Helicoids 16 and 20 are interleaved with one another, occupy the same space and have individual surfaces thereof that are parallel with opposed surfaces of each other to form gaps of large surface area that have equal spacing throughout. Thus, upper surface 17 of helicoid 16 defines a first interelectrode gap 23 with lower surface 21 of upwardly-depending helicoid 20. Similarly, the lower surface 18 of downwardly-depending helicoid 1'6 defines a second continuously parallel interelectrode gap 24 with the upper surface 22 of helicoid 20. First interelectrode gap 23 is electrically in parallel with second interelectrode gap 24. A cylindrical annulus 25 is connected to base member 19 of lower electrode assembly 12 and extends upwardly to lap insulator 14 and to act as a baffle in conjunction with the lower projection 26 of cylindrical sidewall member 13 to prevent the deposition of vaporized or sputtered metallic particles from helicoid arc-electrode members 16 and 20 from being deposited upon insulator and short-circuiting the same. A trigger electrode assembly 27 including a trigger anode 28 and a trigger cathode 29 is mounted in substantially the center of base plate 15 to inject an electron-ion plasma into device 10 when a suitable pulse of electric energy is supplied to trigger lead 30 by a pulsing means 34. A similar trigger assembly 31 having substantially identical parts is adapted to be located at substantially the center of upper planar member 19 to inject a cloud of electron-ion plasma into the volume of device 10 to initiate conduction between arc-electrodes when suitably pulsed in conjunction with trigger electrode assembly 27. Trigger electrode assemblies 27 and 31 may conveniently be the trigger electrode assembly illustrated in Lafferty Patent No. 3,087,092, or the applications of James M. Latferty, Ser. Nos. 516,941; 615,942, and 516,943, all filed Dec. 28, 1965, and assigned to the assignee of the present invention. Means for conmeeting a voltage and/ or an electric load to be switched, protected or otherwise controlled, is provided in the form of terminal lugs 32 and 33 in electrical contact with arcelectrode assemblies 11 and 12, respectively.

Arc-electrode assemblies 11 and 12 are composed of a high purity, high vapor pressure material, as for example, copper or any of the alloys and intermetallic compounds for example set forth in Patent No. 2,975,256 to Lee et a1. and Patents Nos. 2,975,255 and 3,016,436 to I. M. Lafferty and Patent No. 3,140,373 to F. H. Horn, for example, or any similar material which has a sufliciently high vapor pressure to provide conduction carriers in a device which is evacuated to a pressure of 10- tort or less in the quiescent state, and is sufiiciently purified, as for example, by the zone-refining method set forth in Patent No. 3,234,351 to M. H. Hebb, so as to have a concentration of gas and gas-forming impurities of less than one part per million. To aid in maintaining the magnetic field longitudinal at the center of device 10, base members 15 and 19 may, however, be of stainless steel. Sidewall member 13 may be constructed of a high vapor pressure material or may be of a stainless steel or refractory which is out-gassed at sufiiciently high temperatures to preclude the evolution of gasses under arcing conditions, Dielectric 14 may be Pyrex or Vycor glass, or an alumina or fosterite ceramic, for example.

The relationship of the various dimensions of helicoids 16 and 20 should satisfy certain criteria. Thus, for example, the thickness of the metal from which the helicoid turns are formed should be sufficiently large to withstand mechanical stress to prevent deformation. Similarly, the width dimension of the helicoid elements should be large as compared with the thickness thereof in order to provide for stability against deformation and to ensure a large area of interelectrode gap per helicoid turn. Likewise, the outside diameter of each helicoid should be relatively large with respect to the inside diameter thereof, to ensure a broad area of interelectrode gap and a high degree of rigidity. On the other hand, the inside diameter must be sufliciently large as to allow the propagation of a quantity of electron-ion plasma through the space defined by the apertures in all turns, so that substantially unimpeded flow of the discharge-initiating plasma occurs. Additionally, this diameter should be sufliciently large as to ensure essentially azimuthal current paths within each helicoid. Finally, the interelectrode gap 23 and 24 must be the shortest distance between members of opposite polarity to prevent spurious arcing.

While the foregoing dimensional relationships are generally followed, different relationships will exist for different structures depending upon the values of current and voltage at which the device is to be operated, the material from which the helicoids are fabricated, and other criteria such as weight, cost, safety factors, etc. As a guide to specific application of the parameters, however, one typical structure may have an evacuable envelope having an inside diameter of 9" and a longitudinal dimension of 12". Each helicoid therein may be fabricated of OFHC copper and each turn may have a thickness dimension of A The outside diameter of each helicoid may be approximately 6 with an inside diameter of approximately 1". A pitch of approximately one turn per inch for each helicoid, resulting in interelectrode gaps of approximately /2", for example, in the longitudinal direction is suitable. Each helicoid is subtsantially identical to the other with the exception of slight modifications which might occur at the ends thereof, and the device is assembled by winding one helicoid into the other.

In operation, the device is assembled and evacuated to a pressure of torr or less. Electrical contact to a load to be switched, protected, or otherwise controlled and which is subjected to a high voltage of, for example the order of 100,000 volts is made between terminal lugs 32 and 33. When it is desired to render device 10 conductive, a pulse of electric energy, which may for example vary from 50 to 5000 volts, depending upon the interelectrode spacing and the voltage being held off, is applied to trigger electrode assembly 27 or 31, whichever is associated with the negative electrode. If the potential applied between terminals 32 and 33 is alternating, trigger pulses are applied simultaneously to both triggers. Upon the energization of the appropriate trigger electrode assembly, a burst of electron-ion plasma is injected into the center of the helicoids 16 and 20, causing a plurality of conduction paths to be established between the individual turns of the two helicoids and the device becomes conducting. Since the course of conduction currents within the respective electrodes follows the configuration of helicoids 16 and 20, the magnetic field configuration caused thereby is axial, parallel to the longitudinal axis through the two trigger electrodes, as is well know to be the field within a conducting helix. Essentially no magnetic field is present in the interelectrode gaps 23 and 24 between individual turns of the helicoids 16 and 20. If, however, any field does exist in these gaps, such field is parallel substantially to the conduction current paths and the vector product equals or approaches 0, so that no body force acts upon the conducting plasma and there is no bunching of individual current paths, such as to cause the formation of an anode spot, which the attendant erosion and subsequent failure of the device. Additionally, it is to be noted that the electrodes, particularly helicoids 16 and 20, are not likely to be deformed or the interelectrode gap changed, since any force generated by magnetic fields tends to be radial and would be equal and opposite in opposite radial directions of the helicoids. Since the helicoids are very thick from the center of the aperture which runs from trigger electrode assembly 27 to trigger electrode assembly 31 to the outside of the helicoids, they are very rigid and very resistant to any magnetic force which would tend to deform them. Accordingly, the device is quite stable and not subject to transformation during operation.

FIGURE 2 of the drawing illustrates a vacuum switch constructed in accord with another embodiment of the present invention. Since the device of FIGURE 2 is quite similar to the device of FIGURE 1, like members are utilized to identify like parts. In FIGURE 2 vacuum switch 40 includes a first electrode assembly 11 and a second electrode assembly 12 interconnected with a cylindrical sidewall member 13 composed of an insulating dielectric material which may for example be Pyrex or Vycor glass or a high density alumina or fosterite ceramic. First electrode assembly 11 includes a base member 15 and a downwardly-depending helicoid 16, having upper surfaces 17 and lower surfaces 18. Second electrode assembly 12 includes a base member 19 and an upwardlydepending helicoid 20 having lower surfaces 21 and upper surfaces 22. Helicoids 16 and 20 define a pair of parallel interelectrode gaps 23 and 24 which become electrically in parallel when the switch 40 becomes operative. A shield member 41 having a central flange 42 is imbedded in an annular head 43 which is a part of the inner surface of cylindrical sidewall member 13. Shield 41 is utilized to shield a substantial portion of the cylindrical sidewall member 13 from the deposition thereupon of vaporized or particulate metallic coatings which would cause the short-circuiting thereof during the period when switch 40 is in the operating condition. Connection is made between switch device 40 and a circuit to be opened or closed by means of connections to the actuating rods of contact assemblies 44 and 45 which are adapted to make electrical contact between oppositely-poled electrode assemblies 11 and 12. Specifically contact assembly 44 includes a contact 46 connected with an actuating rod 47 which is connected through an hermetically sealed Sylphon bellows 48 and flexible conductive strap to base plate 15 which is a part of electrode assembly 11. Contact 46 is always in electrical contact with electrode assembly 11, and may make or break contact with electrode assembly 12. When the device is in a conducting condition contact 46 is in electrical contact with helicoid 20 at turn 49. When it is desired to establish a conduction path therethrough by virtue of a gaseous discharge, contact 46 is withdrawn from contact with turn 49 of helicoid 20 and an arc is initiated which boils electrode material from the contact surface of turn 49 of helicoid 20. The actuation stroke initiating this action causes contact 46 to be recessed within a recess 50 within plate 15. An electron-ion plasma fills the device 40 as a result of the arc and conduction paths are established in parallel along the entire length of gaps 23 and 24, since these are the closest distances between electrode assemblies 11 and 12. Thus, although the initial arc began at a single point, conservation of energy requires the conduction paths or arcs to spread over the entire surface and the flux paths described hereinbefore with respect to the device of FIG- URE 1 are such as to preclude the further bunching of the conduction paths and the formation of anode spots. The structure of contact assembly 45 at the opposite end of switch 40 is essentially the same as that of contact assembly 44 and its operation is identical. Contact assemblies 44 and 45 serve as the sole or main current connectors to switch 40. A necessary requirement is that each be suitable to sustain the fault current carried until current zero, as is illustrated in FIGURE 2.

In practice, only one contact assembly is essential, but two may be used if the helicoids are very long.

FIGURE 3 of the drawing illustrates an alternative embodiment of the invention illustrating a vacuum gap device having both the characteristics of the triggerable vacuum gap and a vacuum switch. This type device is one having a unique combination of characteristics. Conventionally, it is typical, in utilizing vacuum switches of the reclosable type for protection of a circuit component, as for example, a high voltage capacitor, to shunt the recloser switch across the capacitor and, in the event of an over-voltage, to cause the recloser to close in time to relieve the capacitor from the over-voltage to prevent failure thereof. In practice, it is generally found that the mechanical operation of the recloser requires a suflicient amount of time such that, by the time the recloser has closed to shortcircuit the over-voltage and thereby protect the capacitor or other circuit component being protected, sufificient time has elapsed so that the circuit device, as for example, the capacitor, has been exposed to the over-voltage for a period of time which may cause damage thereto. It is therefore sometimes desirable to shunt the vacuum switch or recloser with a triggerable vacuum gap, thus making it possible to shunt the capacitor or other circuit element being protected by a discharge through the vacuum gap until the recloser has had an opportunity to close. In accord with this embodiment of the invention, one specific structural configuration of which is illustrated in FIG- URE 3, it is possible to cause a single device to function both as a recloser and a triggerable vacuum gap device for protection of circuit components.

In FIGURE 3, a combination circuit protective device 60, embodying both the characteristics of a vacuum switch and a triggerable vacuum gap device, includes an evacuable envelope composed of a first electrode assembly 61, a second electrode assembly 62, a cylindrical sidewall member 13 in hermetic seal between and connecting assemblies 61 and 62 to form an evacuable envelope. First electrode assembly 61 includes a base member 65 and a downwardly-depending helicoid member 66 having an upper surface 67 and a lower surface 68. Second electrode assembly 62 includes a base member 19 and an upwardlydepending helicoid member 70 having a lower surface 71 and an upper surface 72. Helicoids 66 and 70 are interleaved with one another so as to occupy the same space and define therebetween a plurality of parallel interelectrode gaps 73 and 74. First gap 73 is between the lower surface 71 of helicoid 70, and the upper surface 67 of helicoid 66. Second gap 74 is between the lower surface 68 of helicoid 66 and the upper surface 72 of helicoid 70. A substantially cylindrical metallic shield 41 having a central flange 42 is supported with flange 42 supported in a head 43 which is a portion of the inner surface of cylindrical sidewall member 13.

A trigger assembly 27, having a trigger anode 28 and a trigger cathode 29, is mounted upon base member 65 and adapted, upon the application of an electric pulse of, for example 50 to 5,000 volts, from a pulse source 69, to cause the injection of a cloud of electron-ion plasma into the central orifice that exists longitudinally along the helicoids 66 and 70 to cause breakdown therebetween and the conduction of electric currents therebetween. Trigger electrode assembly 27 operates substantially as that described hereinbefore with reference to FIGURE 1 of the drawing. A first terminal lug 32 is connected to a terminal cap member 75 which surrounds trigger electrode assembly 27, and it is of substantially heavy enough construction to provide a sufficiently low electrical resistivity to conduct a main fault current of the order of 50,000 to 100,000 amperes at a very high voltage of the order of 100,000 volts. Alternatively, terminal lug 32 may be made directly to base member 65 at a point along the periphery thereof. It will be appreciated while pulse source 69 is shown as independent of line voltage, it may be adapted to sense an over-voltage therein and be responsive thereto.

A recloser electrode assembly 44 is mounted upon the lower base member 19 of second electrode assembly 62. Recloser electrode assembly 44 includes a contact member 46 which is supported upon an actuating rod 47 and connected in hermetic seal with base member 19 of electrode assembly 62 by a Sylphon bellows 48 and flexible conductive strap 80. Electrode member 46 is adapted to make electrical contact with the lowest turn 49 of helicoid 66 and has a configuration which matches the helicoid at that point so as to mesh in mechanically flush abutment therewith. Contact member 46 may recess into a recess orifice 50 within the helicoid coil in contact with base member 19 so as to become a portion of electrode assembly 62 when in the circuit-open position. Switch contact assembly 44 may be actuated by an upward motion represented by arrow 78 from a means (not shown) to cause the device to be switched into a circuit-closed condition in which contact member 46 seats mechanically and electrically in intimate contact with lower turn 49 of helicoid 66.

In operation vacuum gap device 60 is normally in the circuit-open position or non-conducting condition. It is connected in circuit with a circuit element to be protected, and may for example, be placed in parallel circuit relationship with a capacitor. Upon the occurrence of an overvoltage which would cause the circuit member being protected, as for example, a capacitor, to be subjected to an unnecessarily high voltage which may cause damage thereto, pulse source 69, triggered either independently or by a circuit-sensing means responsive to the over-voltage, supplies a pulse of voltage ranging from 50 to 5,000 volts, for example, depending upon the configuration of the device and the magnitude of the voltage being impressed thereupon, to trigger anode 28. A cloud of ionized electron-ion plasma is ejected from trigger assembly 27 and injected into the interelectrode gaps 23 and 24 between helicoids 66 and 70. Immediately a current path exists from one side of the line at terminal 32 to helicoid 66 across the breakdown gaps 23 and 24 between helicoids 66 and 70 to actuating rod 47 and from a terminal 76 connected thereto to the other side of the line in which the over-voltage occurs. Instantaneously, the circuit element being protected is short-circuited. Simultaneously with the electric signal to pulse source 69, a signal is transmitted to the reclosing mechanism, not shown, to cause the force represented by arrow 78 to be applied in actuating rod 47 to cause contact member 46 to make contact with lower turn 49 and helicoid 66, thus acting as a circuit recloser. For ideal operation with AC two trigger assemblies may be used as in FIGURE 1.

The components of the device 60 of FIGURE 3 may be constructed of the same materials as like components of the devices illustrated and described with respect to FIGURES l and 2 of the drawing. The operation of the trigger assembly section of the device is the same as that described with respect to FIGURE 1 and the operation of the circuit-making and breaking contact assembly 44 is the same as that described with respect to FIGURE 2.

As noted hereinbefore, devices such as that illustrated in FIGURE 3 of the drawing have a unique characteristic of the high voltage protection supported by a circuit recloser simultaneously with the instantaneous operation characteristic of the triggerable vacuum gap. This concept has been described herein with respect to the specific structure illustrated in FIGURE 3 and with respect to the general compound helicoid vacuum gap structure illustrated and disclosed, wherein the unique configuration causes the substantial elimination of magnetic fields within the interelectrode gaps in which electric currents are conducted. This structure is of great value due to the fact that any residual magnetic field which may exist is parallel with the current conduction paths, so that no body force is active upon the conducting plasma and no bunching of conduction paths occurs and formation of anode spots is eliminated. This permits higher current operation, due to the combination of broad area contacts lowering current density and elevation of current threshold for the formation of anode spots.

It will be appreciated, however, that this concept of the combination of the triggerable vacuum gap and the circuit recloser is broader than the specifically illustrated electrode structure. Thus, for example, in my copending concurrently filed application Ser. No. 639,693, a plurality of structures for triggerable vacuum gaps and vacuum switches are disclosed. This application, the entire disclosure of which is incorporated hereinto by reference thereto, has many configurations in which the combination of the triggerable vacuum gap device and the circuit recloser or vacuum switch device may be utilized. Thus, for example, the devices of my aforementioned copending application may be modified by including both trigger electrode assemblies and circuit recloser contacts, the only modification necessary being that the electrical contact to one electrode assembly is made primarily to the circuit recloser electrode which, rather than being merely a contact initiating electrode is made substantially rugged enough as to carry peak overload currents at high voltages as described with reference to FIGURE 3 herein and thus be efiective, not only to initiate breakdown as described therein, but to sustain high overload currents at high voltages.

From the foregoing, it is apparent that I have disclosed a new and unique configuration for electrodes for triggerable vacuum gap devices and vacuum switch devices composed of interleaved helicoids which provide broad area contact with broad area interelectrode gaps and a configuration which eliminates substantially all magnetic fields from the interelectrode gap to prevent bunching of conduction paths therein and the formation of anode spots. Similarly, I have disclosed the concept of the combination of the characteristics of a triggerable vacuum gap device and a vacuum switch specifically of the recloser type wherein a single device may utilize the characteristics of both to provide a single circuit protective device which may be operated instantaneously as the triggerable vacuum gap device and may have the recloser characteristics of the vacuum switch or circuit recloser.

More specifically, such a device embodying this particular feature of the present invention utilizing an electrode configuration disclosed more specifically in the aforementioned application, 639,693, is illustrated in FIGURE 4 and comprises an evacuable envelope 13 including a first outer cylindrical arc-electrode assembly 61 and an inner reentrant cylindrical arc-electrode assembly 62 concentric with arc-electrode assembly 61. A pair of terminal lugs 32 and 33 are utilized to connect the device in circuit with an electric load or circuit to be protected. The device may be utilized as a recloser in which trigger electrode assembly 27 is utilized, as is described hereinbefore, to inject a pulse of ionized particles into the inter-electrode gap between arc-electrode assembly 61 and 62 while recloser electrode assembly 44 is used mechanically to establish physical and electrical contact therebetween by means of recloser electrode 46 actuated by actuating rod 47, which is electrically connected with arc-electrode assembly 62 by means of flexible conductive strip 80.

While the invention has been set forth herein with respect to specific embodiments and particular examples thereof, many modifications and changes will readily occur to those skilled in the art. Accordingly, I intend by the appended claims to cover all such modifications and changes as fall within the true spirit and scope of the present invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A vacuum gap device adapted to conduct high electrical currents without the formation of anode spots and comprising:

(a) an evacuable envelope evacuated to a pressure of torr or less including at least a portion of which comprises a high voltage insulator (b) first and second electrode members within said envelope and defining therebetween at least one interelectrode gap (b said electrode members having the configuration of a pair of interleaved helicoids defining substantially equal interelectrode spacings along the length thereof (c) means within said envelope for supplying an electron-ion plasma to cause said interelectrode gaps to become conducting to switch said device from a non-conducting to a conducting state (d) and means for connecting said electrode members in circuit with an electric load.

2. The device of claim 1 wherein each of said helicoids is constructed of a wound flat plate of electrode material the width of which is large with respect to its thickness dimension.

3. The device of claim 2 wherein the inner diameter of said helicoids is small as compared with the outer diameter thereof to provide a very broad area of electrode surface for interelectrode conduction.

4. The device of claim 1 wherein said means for supplying a quantity of electron-ion plasma within said device comprises a trigger gap assembly adapted to produce and ionize vaporizable conducting material upon the application of an external electrical signal.

5. The device of claim 1 wherein said means for supplying a quantity of electron-ion plasma within said device comprises means for making and breaking contact directly between said electrodes.

6. A circuit protective vacuum gap device comprising:

(a) an evacuable envelope evacuated to a pressure of 10 torr or less and including as a portion thereof a high voltage dielectric,

(b) a pair of primary arc-electrodes therein defining therebetween a broad area interelectrode gap, and comprising a pair of parallel interleaved helicoids which are concentric with the same longitudinal axis,

(0) trigger assembly means associated with one of said electrodes and adapted to inject a quantity of electron-ion plasma into said interelectrode gap to render said device electrically conducting, when pulsed with a signal voltage (d) movable contact electrode means adapted to effect direct metallic contact between said primary arcelectrodes subsequent to the actuation of said trigger assembly means, and

(e) means for connecting said primary arc-electrodes in circuit with an electrical load.

7. The device of claim 6 wherein in the interelectrode gap the quantity is substantially zero where is the current density within the interelectrode gap and is the magnetic flux density within the interelectrode gap.

8. A circuit protective vacuum gap device comprising:

(a) an evacuable envelope evacuated to a pressure of 10* torr or less and including as a portion thereof a high voltage dielectric;

(b) a pair of primary arc-electrodes therein defining therebetween a broad area interelectrode gap, having shape and configuration that substantially no magnetic field having a component normal to current conduction paths between said primary arc-electrodes exists within said interelectrode gap and the formation of anode spots due to conduction paths bunching within said interelectrode gap is substantially eliminated,

(b said primary arc-electrodes comprising an inner re-entrant cylinder and an outer concentric cylinder so that current conduction in said arcelectrodes is substantially parallel to a longitudinal axis thereof;

(c) trigger assembly means associated with one of said electrodes and adapted to inject a quantity of electron-ion plasma into interelectrode gap to render said device electrically conducting, when pulsed with a signal voltage;

(d) movable contact electrode means adapted to effect direct metallic contact between said primary arc- JAMES LAWRENCE, Prlmafy EXaminel' electrodes subsequent to the actuation of said trigger R. HOSSFELD, Assistant Examiner assembly means; and (e) means for connecting said primary arc-electrodes 5 us CL X 1n circult Wlth an electrical load. 313x198, 315111 References Cited UNITED STATES PATENTS 3,356,893 12/1967 Lafferty 3151 11 

